For many years, can manufacturers have been producing cans having the familiar ring-pull and removable section which could be completely severed from the remainder of the container. Examples of end panels of containers having this type of removable section are disclosed in U.S. Pat. No. 3,445,029 and 3,428,210.
Since the container industry produces at least 46 billion cans annually for packaging soft drink and beer, millions of these tear strips and tabs are left on beaches, parks, along highways and in campgrounds each year and these are not only unattractive but area also considered dangerous.
Thus, for nearly a decade, the can industry has attempted to develop non-detachable substitutes for the familiar pull-tab cans. One type of substitute that has been proposed is known as the "button" design wherein a weakened area is defined in the end panel of the container and the entire button is severed from the end panel and drops into the container. Examples of this type of substitute are shown in U.S. Pat. Nos. 3,902,626; 3,902,627; and 3,982,657. The main problem with this type of design is that considerable pressure must be exerted to sever the weakened line when a pressurized carbonated beverage is packaged in the container. This type of container is also considered in some respects to be unsanitary since the "button" drops into the contents. One type of design which has been proposed in this category includes two openings in the end panel of different size, one providing a venting feature and the second for a pouring opening. This arrangement creates an additional problem in that the smaller "button" may come out of the larger hole with the contents. A further problem encountered with this type of closure or end panel is that the user may cut his finger during severing of the "button."
As a further alternative to the well known ring-pull tab, various other types of end panels have been proposed wherein a tab type unit is utilized for fracturing a weakened line and the tab is then used in supporting the severed portion on the container panel. This type of arrangement is disclosed in U.S. Pat. No. 3,236,409.
Other types of end closures have been proposed wherein the severed portion remains permanently attached at at least a localized area after fracture of the weakened area. Examples of this type of unit are disclosed in U.S. Pat. Nos. 3,946,683; 3,934,750; and 3,874,555.
While there have been literally dozens of proposed substitutes for the familiar severable tear strip with the attached tab, none of the proposed substitutes has received any substantial degree of commercial success because they are either too complicated to operate, too expensive to produce or are unsanitary during use. Thus, there remains a need for a non-detachable opening device which is capable of withstanding a required pressure without leaking, and also is capable of meeting the minimum pressure requirements with respect to "buckling" and "rock."